Method checkIterator

Tests/HashTreeTests.cc:84–93

    }

    void checkIterator(size_t N) {
        set<slice> keysSeen;
        for (MutableHashTree::iterator i(tree); i; ++i) {
            //cerr << "--> " << i.key().asString() << "\n";
            CHECK(keysSeen.insert(i.key()).second); // insert, and make sure it's unique
            REQUIRE(i.value() != nullptr);
            CHECK(i.value().type() == kFLNumber);
        }
        CHECK(keysSeen.size() == N);
    }

    alloc_slice encodeTree() {
        Encoder enc;